The present invention relates to a valve arrangement, in particular for an expansion valve of a refrigeration system, the capacity of which is determined by pulse width modulation. This means that within a cycle of for example 6 seconds the valve is opened, in particular electromagnetically, for a specific fraction, for example 4 seconds, and closed for the remaining fraction, that is, in this example 2 seconds. The ratio of the opening time to the closing time determines the degree of opening of the valve and thus the mass flow through the valve.
Valves of this kind are already known and are used in refrigeration circuits instead of the usual thermostatic expansion valves. In this these valves can serve not only as an expansion valve, but also as a closure valve. A separate closure valve is thus not required.
A problem in valves of this kind as a result of the frequent change between the open position and closure position is the so-called water hammer effect, that is, the shock waves resulting from the rapid opening and/or closing. It is therefore already known to provide a damping device. For this the space between the movable valve armature and the stationary armature core is formed as a damping chamber in that the space between the movable valve armature and the armature tube surrounding the latter is formed as a throttling passage. In this a brass sleeve which is finished to a pass fit is inserted into the armature tube, which is usually manufactured of steel, and surrounds the movable armature at such a distance that the medium can escape from the damping chamber only at a desired speed.
In accordance with the invention it is now provided, instead of a sleeve, to form the armature tube itself as a pass fit tube, in particular in that a precisely machined bore is introduced into the armature tube. In this the armature tube is manufactured of a suitable material, for example brass. The armature core of magnetic iron is then inserted into the armature tube and secured to the latter for example through hard soldering. This execution is advantageous in regard to the manufacturing technique, since a turned brass part can be used, whereas in the use of a sleeve for the pass fit damping a comparatively thin tube must be used. In addition this tube must be inserted into the conventional armature tube, for which the conventional armature tube must be manufactured with sufficient measurement precision and an additional step is required in the manufacture.
Furthermore, it is also advantageous when the armature tube and preferably also the movable armature are finished to a pass fit only over a region of their surfaces. Through this a sufficient pass fit for achieving the desired damping can be attained with a low cost and complexity.
Furthermore, it is advantageous when securing means are formed on at the armature tube, through which the armature tube can be connected to the valve housing. In particular the armature tube can be provided with an outer thread. A separate component is thereby saved. In all there results thereby a reduction of the required components from four to two, namely instead of an armature tube, a securing means such as a hexagonal nut, an armature core and a pass fit sleeve now only an armature tube with an outer thread and an armature core are required. In this the armature core can be designed such that it can be used in addition for securing the magnetic coil to the armature; for example a circumferential groove can be provided in its periphery into which a securing means, for example a bracket, engages.
The valve in accordance with the invention is preferably executed as a slider valve. This has the advantage that friction which arises on the seating surface with the valve opening during the displacing of the slider element additionally damps the movement of the valve. In addition the slider is pressed onto the counter-surface by the refrigerant medium, which is under pressure, when the valve is used as an expansion valve in a refrigeration circuit. Through this on the one hand the frictional force is increased and on the other hand a reliable complete closing is ensured. A further advantage with respect to an axially seated valve consists in that the armature is not sucked onto the valve seat as a result of the pressure conditions which are present when the valve is closed. The water hammer effect is further reduced thereby.
Synthetic material, including ceramic, is preferably used for the slider and/or for the counter-surface. In particular silicon carbide and aluminum oxide have each proved advantageous, with it being possible either for both elements to be manufactured of the same material or one each of them of one of the two materials. With these materials very even planar surfaces can be produced. In addition, in contrast to metal, there is no danger of corrosion. The use of silicon carbide and/or aluminum oxide in contrast to the use of Teflon has the advantage that through the named materials no metal particles which are possibly present can be accumulated. Through the named materials therefore an improved inner imperviousness of the valve can be achieved. This is important in particular in regard to the closing function in order to achieve energy losses which are as low as possible.
In the valve in accordance with the invention it is preferably observed that the ring gap between the armature tube and the movable armature is not chosen too small in order to avoid a gas resiliency effect. Such a strong damping could lead to an alternating current vibration of the valve.
A restoring spring is preferably provided for restoring a movable armature. The former is in particular provided between the movable armature and the armature core and, likewise preferably, accommodated at both ends in blind holes. This arrangement and embodiment simplifies the assembly. Through the use of a spring of small cross-section and without a great buckling stability a rotatability of the movable armature can be achieved in addition. The wear of the movable armature is thereby advantageously reduced. Accordingly, it is preferred to support the slider at the movable armature in such a manner that the movable armature is rotatable, in particular largely freely rotatable. For this the movable armature can be provided with a reception groove at its periphery in which the slider, which is reciprocally formed thereto at its facing side, is supported. The lifetime of the movable armature can be thereby increased.
A further improvement results in that the passage opening in the counter-surface to the slider is formed in the direction of movement of the slider in such a manner that the opening is only slowly freed at first and then increasingly rapidly. In particular the opening cross-section can be designed to run together in a pointed manner in the direction of movement of the slider, that is, in such a wedge-like manner that at first only a wedge tip is freed by the slider. Through this an abrupt change between a completely closed and an opened passage opening is avoided. Through this the water hammer effect is also further reduced.
A further improvement results in that a further opening with selectable cross-section is provided in addition to the passage opening in the counter-surface. The capacity of the valve can thereby be varied via the choice of this second opening, which can be provided in a special insert. This is particularly economical, in particular also in stocking, since all remaining constituents of the valve are the same for different capacities.
It is particularly preferred when the additional passage opening is formed as a replaceable exchange nozzle, which can in particular be screwed together with the valve housing. With this the capacity of the valve can be changed in a simple manner through replacement of the exchange nozzle. If the exchange nozzle is arranged behind the passage opening of the counter-surface a replacement directly via the connector piece is possible, so that the replacement can be carried out without opening the valve. It is merely necessary to unscrew the exchange nozzle out of the valve housing from the outlet side and to screw in another, desired nozzle.